Conical hybrid FDB motor

ABSTRACT

A disc drive design comprising a shaft and sleeve supported for relative rotation by a journal type fluid dynamic bearing utilizing grooves on one of the shaft or sleeve surfaces. At least a part of the shaft is generally conical in cross-section, so that a downward force component is developed to balance upward pressure on end of shaft; this conical region typically includes a fluid dynamic bearing (grooves being on either the shaft or sleeve). A grooved pattern of a design similar to that usually found on a thrust plate may be defined on an axial end surface of the shaft or the counterplate facing the axial end of the shaft, so that thrust is created to maintain separation of the end of the shaft and the facing counterplate plate during relative rotation. A diamond-like coating (DLC) may be applied to the counterplate surface or to the end of the shaft; further, either the counterplate or shaft may be made out of ceramic material to enhance this performance. This coating may also be applied to the conical surface of the shaft or the facing surface of the sleeve.

CROSS REFERENCE TO A RELATED APPLICATION

[0001] This application claims priority to a provisional applicationserial No. 60/342,681 filed Dec. 20, 2001, in the names of AnthonyJoseph Aiello, Klaus Dieter Kloeppel and provisional application ______filed Nov. 5, 2002, in the names of Jeffry Arnold LeBlanc, Alan LyndonGrantz, Troy Michael Herndon, Michael David Kennedy, Robert AlanNottingham, entitled Single Core FDB Motor for HDD Applications, whichapplication is incorporated herein by reference.

FIELD OF THE INVENTION

[0002] This invention relates to fluid dynamic bearing motors, and moreparticularly to such motors without thrust plate.

BACKGROUND OF THE INVENTION

[0003] Disc drive memory systems have been used in computers for manyyears as storage space for digital information. Information is recordedon concentric memory tracks of magnetic discs that rotate around aspindle. Information is accessed by read/write heads located on apivoting arm which moves radially over the surface of the disc. Theread/write heads (-transducers-) must be accurately aligned with thestorage tracks on the disc to ensure proper reading and writing ofinformation.

[0004] The discs are rotated at high speeds in an enclosed housing bymeans of an electric motor located inside the hub or below the discs.Such a motor is commonly known as a spindle motor. Such spindle motorstypically have a spindle mounted by means of two ball bearing systems toa motor shaft in the hub. One of the bearings is located near the top ofthe spindle and the other near the bottom. These bearings allow forrotational movement between the shaft and the hub while maintainingaccurate alignment of the spindle and the shaft. The bearings arenormally lubricated by grease or oil.

[0005] The conventional bearing system described above is prone,however, to several shortcomings. First, vibration is generated by theballs rolling on the raceways. Ball bearings used in hard disk drivespindles run under conditions that often cause physical contact betweenraceways and balls in spite of the lubrication layer provided by thebearing oil or grease. Hence, ball bearings running on the apparentlyeven and smooth, but microscopically uneven and rough, raceways transmitsurface and circular imperfections in the form of vibration to therotating disk. This vibration results in misalignment between the datatracks and the read/write transducer. These imperfections reduce thelifetime and effectiveness of the disc drive system.

[0006] Another problem is related to the use of hard disk drives inportable computer equipment and the resulting requirements for shockresistance. Shocks create relative acceleration between the disks andthe drive casting. Since the contact surface in ball bearings is verysmall, the resulting contact pressures may exceed the yield strength ofthe bearing material and leave permanent deformation and damage onraceways and balls.

[0007] Moreover, mechanical bearings are not always scaleable to smallerdimensions. This is a significant drawback since the tendency in thedisc drive industry has been to continually shrink the physicaldimensions of the disc drive unit, as well as operate the units atever-increasing speeds.

[0008] Another problem is that of potential leakage of grease or oilinto the atmosphere of the disc drive, or outgassing of the componentsinto this atmosphere. Because of the extremely high tolerance requiredfor smaller radial spacing between tracks on the disc and the gap in thetransducer which is used to read and write data on the disc, discs arelocated within sealed housings in which contaminants cannot betolerated.

[0009] As an alternative to conventional ball bearing spindle systems,hydrodynamic bearing spindle systems have been developed. In these typesof systems, lubricating fluid (gas or liquid) functions as the bearingsurface between a stationary base housing and the rotating spindle/hub.For example, liquid lubricants including oil, more complexferro-magnetic fluids, or even air have been utilized in hydrodynamicbearing systems. Air is popular because it is important to avoid theoutgassing of contaminants into the sealed area of the head dischousing. However, air cannot provide the lubricating qualities of oil orthe load capacity. Its low viscosity requires smaller bearing gaps andtherefore higher tolerance standards to achieve similar dynamicperformance. The liquid lubricant must be sealed within the bearing toavoid a loss which would result in reduced bearing load capacity andlife. Otherwise, the physical surfaces of the spindle and of the housingwould come into contact with one another leading to accelerated wear andeventual failure of the bearing system.

[0010] In the prior art, seals for containing the fluid within the discdrive utilize a pressurized film on the surface of the liquid-airinterface, or surface tension. In the case of bearing assemblies whichemploy ferro-magnetic fluids, the seal is achieved by means of amagnetic field established at each end of the bearing.

[0011] A shortcoming of known hydrodynamic bearings includes the factthat many prior art hydrodynamic bearing assemblies require large orbulky structural elements for supporting the axial and radial loads, asmany hydrodynamic bearings do not have the inherent stiffness ofmechanical bearing assemblies. It is difficult to scale the structuralsupport elements to fit within the smaller disc drive dimensionscurrently in demand. In other instances, hydrodynamic bearing assembliesrequire extremely tight clearances and precise alignments. This burdenmakes it difficult to manufacture such assemblies since even a smalldeviation or aberration can lead to faulty bearings. Further, as thegaps in which the fluid is located become smaller, the power consumed torotate the spinning elements.

[0012] Another consideration is that the data track density on harddiscs has been decreasing, and track mis-registration, commonly known asTMR, is becoming increasingly critical. One of the primary contributorsto TMR is disc spindle runout. It consists of both repeatable runout andnon-repeatable runout, commonly referred to as NRRO. The NRRO of a ballbearing motor is often too high for today's disc drives. However, fluiddynamic bearings (FDB) provide a much lower NRRO, which better supportsthe high aerial data densities of current disc drive technology.

[0013] The architecture of fluid dynamic spindles in the past hasgenerally included a shaft in a housing, which provides radialstiffness, and a thrust bearing, which controls the vertical position ofthe spindle. Both the shaft and thrust bearing have generally beencushioned by a fluid film. The journal and shaft surfaces have typicallybeen provided with miniature grooves, which create pressure by directingthe fluid into specific areas of the journal.

[0014] One problem with this conventional FDB spindle motor arrangementis that it limits the degree to which the height of the motor assemblymay be reduced. This is because the thickness of the thrust bearing mustbe added to the length of the shaft, which itself must be of a lengthsufficient to provide rotational stability. Moreover, use of a thrustbearing increases the amount of drag the motor must overcome duringoperation, increasing power consumption.

[0015] In the field of fluid dynamic bearing motors for use in hard discdrives, some prior systems including, but not limited to, small formfactor motor designs for mobile applications have been limited bystringent power requirements. In the traditional “single-plate” FDBdesign, a thrust plate with two equal and opposing thrust bearings isaffixed to the journal bearing shaft to provide axial stiffness. Thisapproach results in bear gaps at large diameters, thereby increasingbearing drag and overall motor power.

SUMMARY OF THE INVENTION

[0016] It is an objective of the invention to provide a hydrodynamicbearing which is simple and scalable in design, which diminishes theamount of power consumed during rotation while maintaining dynamicperformance under operating vibration conditions.

[0017] It is another objective of the invention to diminish the powerlosses or power consumption associated with use of the thrust platemounted on a shaft.

[0018] It is a related objective of the invention to provide a reductionin the overall height of the motor by elimination of the thrust plate.

[0019] Another objective of the invention is to reduce the drag and makethe motor more efficient while permitting operation using lower power byelimination of the thrust plate.

[0020] Another objective of the invention is to provide a bearing designfor use in a spindle motor which also is designed to prevent separationof the parts of the bearing when the motor is inverted or subjected toshock, even lacking a thrust plate.

[0021] Another objective in certain embodiments is to increase thejournal span for angular response improvement.

[0022] These and other objectives of the invention are achieved in thedesign comprising a shaft and sleeve supported for relative rotation bya journal type fluid dynamic bearing utilizing grooves on one of theshaft or sleeve surfaces. At least a part of the shaft is generallyconical in cross-section, so that a downward force component isdeveloped to balance upward pressure on end of shaft; this conicalregion typically includes a fluid dynamic bearing (grooves being oneither the shaft or sleeve).

[0023] In many embodiments a grooved pattern of a design similar to thatusually found on a thrust plate is defined on an axially end surface ofthe shaft or the counterplate facing the axial end of the shaft, so thatthrust is created to maintain separation of the end of the shaft and thefacing counterplate plate during relative rotation.

[0024] In yet another alternative embodiment, to provide furtherrobustness to the start/stop induced wear which is created by frictionbetween the end of the shaft and the facing counterplate, a diamond-likecoating (DLC) may be applied to the counterplate surface or to the endof the shaft; further, either the counterplate or shaft may be made outof ceramic material to enhance this performance. This coating may alsobe applied to the conical surface of the shaft or the facing surface ofthe sleeve.

[0025] Other features and advantages of the invention may be apparent toa person of skill in the art who studies the following description ofpreferred embodiments given with reference to the figures brieflydescribed below.

[0026] In another embodiment, a recirculation or pressure equalizationport is provided from the gap between shaft end and counterplate to aregion between the conical bearing and journal bearing; this partprovides means for equalizing pressure across the cone and/or providesmeans to eliminate air bubbles from fluid in the shaft end/counterplategap.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is a perspective view of a disc drive in which the presentdesign is useful;

[0028]FIG. 2 illustrates the current single thrust plate design;

[0029]FIG. 3A illustrates an embodiment of the present invention;

[0030]FIG. 3B illustrates one of several potential groove patternsuseful on the surface of the counterplate 310 of Figure A;

[0031]FIG. 4 embodiment with full-length conical shaft.

[0032]FIG. 5 illustrates a further alternative embodiment of theinvention;

[0033]FIG. 6 illustrates yet another embodiment of the invention;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] The following description of a preferred embodiment of theinvention is given with reference to its use in a disc drive, since discdrives are especially directed to incorporating motors of a low profile.However, the present invention may also be useful in many other formatsand environments.

[0035] Thus, as an exemplary environment for use in the presentinvention, FIG. 1 shows an exploded perspective view of a disc drivestorage system in which the present bearing and motor would be useful.FIG. 1 is provided primarily to give an illustrative example of theenvironment in which a motor incorporating the bearing comprising thefeatures of the present invention is used; clearly, the motor could beused equally well in other designs of disc drives, or other operatingenvironments apart from disc drive technology where minimizing the startand run power for the motor, and/or minimizing the overall height of themotor is a desirable feature.

[0036] More particularly, in FIG. 1 the storage system 10 includes ahousing 12 having a spindle motor 14 which rotatably carries the storagedisc or discs 16. An armature assembly 18 moves transducers 20 acrossthe surface of the discs 16. The environment of discs 16 is sealed byseal 22 and cover 24. In operation, discs 16 rotate at high speed whiletransducers 20 are positioned at any one of a set of radiallydifferentiated tracks on the surface of the discs 16. This allows thetransducers to read and write encoded information on the surface of thediscs at selected locations. The discs rotate at very high speed,several thousand rpm, in order to maintain each transducer flying overthe surface of the associated disc. In present day technology, achievingthe high speed of rotation and maintenance of that high speed whileutilizing minimum power is a very important goal.

[0037] A common characteristic of the reduced power fluid dynamicbearing design of the invention is the provision of a fluid dynamicbearing (FDB) without the traditional thrust washer or plate, but rathercomprising a grooved thrust bearing defined between the end of the shaftand the opposing counterplate, and an opposing means comprising at leastone conical journal bearing for establishing a counter force in order tomaintain the alignment of the relatively rotating parts in the system.

[0038]FIG. 2 illustrates the basic elements of a basic currenttechnology single thrust plate design comprising a shaft 200 having athrust plate 202 at an end thereof facing a counterplate 204. The shaft200 and thrust plate 202 are supported for rotation relative to thesleeve 210 by a journal bearing 212 defined by grooves on one of theshaft 200 or sleeve 210 and fluid in the gap 214 between those twosurfaces. The rotation of the shaft and thrust plate is furthersupported by thrust bearings defined between the axially facing surfaces230, 232 of the thrust plate 202 and the facing surfaces of counterplate 204 and sleeve 210. Rotation of the shaft and thrust plate withinthe sleeve is established in accordance with well known principles byenergization of the coils 240 of the stator in cooperation with themagnet 242.

[0039] A first embodiment of the present invention can be found in FIG.3A, with a particular feature, that is an example of the grooved designwhich is located between the shaft end and counterplate, i.e., on thebase of the shaft facing the counter plate, base plate or equivalent,(or vice-versa, on the counterplate surface) to support relativerotation of the shaft and sleeve being shown in FIG. 3B.

[0040]FIG. 3A shows a rotating shaft 300 supporting a hub 302 forrotation with the shaft. The hub 302 is clearly adapted to support oneor more discs (not shown) on the shoulder 304 for constant high speedrotation. This rotation is established by the stator 310 which ismounted from the base cooperating with the magnet 312 which is mountedfrom the inner surface of the hub 302.

[0041] It can be seen that the end face 321 of the shaft which isdefined at the end of the conical cross-section faces upper surface 323of counterplate 310. Either the base surface 321 of the shaft or thefacing counterplate surface 316 includes a grooved pattern 322 thereonas shown for example in FIG. 3B. Fluid is introduced into this gap underthe urging of the grooved pattern 322 when the shaft starts spinningfrom the gap 330 between the shaft 300 and the surrounding sleeve 336.This fluid is drawn into the shaft end and counter-plate thrust bearingregion 325 to support relative rotation between the end of the shaft andthe facing surface of the counterplate, the fluid being maintained inthe gap 325 by the grooved pattern during rotation.

[0042] A journal bearing 354, as is well known in this technology isdefined on the outer surface 350 of the shaft or the facing surface 352of the sleeve utilizing the fluid in gap 330. This journal bearing 354would have the dual function of supporting the shaft for rotation, and,if biased to accomplish this goal, could also tend to force fluid fromthe gap 330 toward the shaft/counterplate gap 325.

[0043] To this end, the journal bearing in the gap 330 could be definedwith the grooves proportioned to create a downward bias toward the shaftend and/counterplate bearing 340 at gap 325. This journal bearing 354aids in moving fluid from the journal gap 330 toward the thrust gap 325especially at start-up and maintains it during continuous runningconditions. To prevent the shaft from being displaced axially too farfrom the counterplate, by the axially upward thrust bearing at gap 325between the shaft end and counterplate, an opposing bias is typicallyintroduced. This bias is utilized to prevent the gap 325 from becomingtoo large, which would reduce the effectiveness of the shaft thrustbearing at gap 325.

[0044] For this reason, the journal bearing defined on the conicalcross-sectional surface 352 of shaft 300 is provided. This journalbearing, since it appears on a conically-tapered surface, will have adownward thrust component in the direction of arrow 360, which actsagainst the upward force component 362 which is generated by therelative rotation of the thrust bearing created by shaft end surface 321and counterplate surface 323. The provision of this downward force keepsthe system balanced for optimum gap widths and rotation. This groovepattern may also be biased to move fluid toward the shaft end.

[0045] It may be beneficial to also introduce an electromagnetic bias,as for example, by offsetting the magnet 312 relative to the stator 310or by mounting small magnets on the upper surface of sleeve 336 facing amagnet on a lower surface of the hub 302 to introduce a means to biasthe shaft either axially toward the counterplate or away from thecounterplate upon landing when the operation of the motor ceases. As anadditional feature, then a wear-tolerant surface such as DLC or the likewould be introduced to establish a wear-tolerant landing zone. Forexample the inner surface 330 of sleeve 336 (or the outer surface of theconical shaft section) may have a wear tolerant layer if the bias isupward in the direction of the arrow 362. Upon landing, the rotatingshaft would land and start up against a wear tolerant surface. A similarsurface could be on the end of the shaft or the facing counterplatesurface in which case an opposite bias needs to be established.

[0046] In the embodiment of FIG. 3A, at least a section 350 of the shaft300 is tapered outwardly at its outer surface 350 and the inner surface352 of sleeve 336 is also tapered to establish a fluid bearing gap 330.A groove pattern which may be of any type known in this field is definedon this tapered surface, and is of sufficient length to create an axialcomponent of force downward toward the counterplate 310 to balance theupward force which is being exerted axially against the lower face 321of shaft 300. The axial component of the fluid bearing defined along theconical surface 352 tends to drive the shaft down toward thecounterplate in the direction of the arrow 360 thereby counteracting theforce exerted against the surface 321 by the pumping action of the fluidbearing 322 which tends to drive the shaft axially up away from thecounterplate in the direction of the arrow 362.

[0047] Yet another alternative appears in FIG. 4 in which the entirelength of the shaft 400 with which the hub 402 is supported, is taperedas shown. This approach is potentially easier to manufacture because theentire outside surface 404 of shaft 400 can easily be tapered with agrinding process; the inner surface 406 of sleeve 408 could be preparedin a similar way to establish the gap 410 for the fluid bearing 412. Inthis design, grooves at least one or more groove sections 416, 418 aredefined on the outer surface 404 of the shaft. Due to the angled surfaceof the journal a force is created which tends to drive the rotorcomprising shaft 400 down toward the counterplate 420, therebyoffsetting the upward biasing force against the surface 421 of the shaft400. This upward bias is created by a grooved pattern on either thesurface 421 on the bottom of the shaft 400 or, preferably, a similarpattern on the shaft facing surface 424 of counterplate 420. In a mannersimilar to the embodiment of FIG. 3, the groove patterns 416, 418 on theouter surface 404 of shaft 400 can be asymmetrical to establish anaxially downward bias 430 toward counterplate 420.

[0048] A further embodiment of the invention is shown in FIG. 5 which isa design including a fixed shaft 500 supported from a base 502. Thedistal end 504 of the shaft includes a cone 506 which may be eitherfastened to the shaft or integrally formed on the shaft. In this design,an asymmetric journal bearing 510 is provided which pumps fluid towardthe conical end of the shaft. One of the two surfaces facing the conicalgap 520, i.e., either the outer surface 522 of the conical region 506 orthe facing surface 524 of the sleeve 526 also have grooves to supportthe rotation of the sleeve 526 about the fixed shaft 500.

[0049] The end of the bearing system distal from the asymmetric journalbearing includes a gap 530 defined between the counterplate 532 and theend surface 534 of the shaft 500 including conical 506. The asymmetricbearing 510 can be established to pump with sufficient pressure throughthe continuous gap 520 which includes the journal bearing 510 andconical bearing 520 as well as the end gap 530 to provide a hydraulicpressure against the end of the shaft 534. If the asymmetric journalbearing 510 pumps with sufficient pressure, this asymmetry aloneprovides a sufficient hydraulic pressure and axial thrust in thedirection of arrow 540 to set the bearing gap 530 and thereby the gapfor the conical bearing 520 for this bearing to effectively operate inhigh-speed rotational operation.

[0050] Alternatively, the gap region 530 could include a groove patternas shown in FIG. 3B and described with respect to FIGS. 3A and 3B. Thiswould establish a thrust bearing to create axial force in the directionof arrow 540 that works either alone or in conjunction with thehydraulic force to set the bearing gap in the region of conical bearing520.

[0051] In yet another embodiment, the end of the shaft read gap region530 could include a thrust bearing where the gap 530 is potentiallyfairly large. In such a region, grooves would be provided on either endsurface 534 of the shaft or the facing surface 544 of the counterplatewhich as the shaft begins to rotate would help initially lift the shaftby generating force in the direction of the arrow 540. But this forcewould diminish as the hydraulic force increases the gap with increasingspeed, setting the conical gap but efficiently reducing the requiredrunning power for the motor.

[0052] Each of these embodiments utilizes a recirculation path 550comprising one or more openings or ports extending from the gap 530defined between counterplate 532 and its surface 544 and the facingsurface 534 of the shaft end, and extending to a point between theconical bearing 520 and the journal bearing 510. This equalization pathfrom gap 530 to 0.552 tends as its name implies to equalize the pressureat both ends of the gap, that is, the same pressure exists both aboveand below the cone. This tends to create a more stable operation for theoverall system. The equalization path is defined simply by providing oneor more generally axially directed openings 550 from the gap 530 to thejunction 552.

[0053]FIG. 6 shows an embodiment incorporating similar principals asapplied to a rotating shaft design. In this design, the rotating shaft600 supports a hub 601 at an end thereof and includes a cone 602 at anend adjacent the counterplate 604. The shaft 600 and cone 602 aresupported for rotation by an asymmetric journal bearing 606 which pumpsto create a pressure gradient in the direction of arrow 608 and aconical bearing 610 defined by grooves on one of the surfaces 612, 614which face each other across the gap 610 and are defined in accordancewith known principles. The fluid bearing system further comprises a gap620 between an axially facing surface 622 of counterplate 604 and acooperating surface 626 defined at an end of the shaft 600 and cone 602.This gap region may or may not include grooved features, depending uponthe operating principles of the design as described above. That is, thejournal bearing asymmetry can be defined to provide a hydraulic pressureagainst the end 626 of the shaft, with this pressure alone providing anaxial thrust that sets the bearing gap for the conical bearing at gap610. Alternatively, the end of the shaft would include a thrust bearingby defining grooves on one of the surfaces 622, 626 pumping toward thecenter of the shaft thereby providing an axial force in the direction ofarrow 630 that works with the hydraulic force established by theasymmetric bearing to set the bearing gap for the conical bearing 610.Yet in another embodiment, the end of the shaft would include a thrustbearing with a potentially relatively large gap 620 such that the axialforce would initially help lift the shaft off surface 626 off the facingcounterplate surface 622; but the force would diminish as the hydraulicforce increases the gap with increasing speed, thus reducing the runningpower of the motor. Each of these approaches would preferably utilizeone or more equalization ports 650 which equalized the pressure betweenthe gap 620 and the common region 660 between the conical bearing 610and the journal bearing 606. These ports which simply comprise one ormore openings connecting the two regions equalize the pressure at bothends of the opening functioning as the equivalent of a short circuit toget equal pressure above and below the cone to stabilize the cone.

[0054] Other features and advantages of this design may be apparent to aperson of skill in the art who studies the above disclosure. Therefore,the scope of the invention is to be limited only by the followingclaims.

[0055]FIG. 7 illustrates schematically a further alternative to theabove designs wherein the conical bearing is distal from the shaft endgap which serves as a thrust bearing.

What is claimed:
 1. A fluid dynamic bearing comprising a shaftsupporting a hub at one end, the shaft being adapted to rotate within asleeve supported from a base, the base including a counterplate facingan end of the shaft distal from the one end on which the hub is mounted,the shaft being supported for rotation within the sleeve by a journalbearing comprising fluid in the gap between the shaft and the sleeve,one of the distal end of the shaft or the surface of the counterplatewhich faces the end face of the shaft having a grooved pattern thereonto maintain fluid in the gap between the shaft and the counterplate,thereby supporting the shaft for rotation relative to the counterplateand sleeve, at least part of the shaft being conical in cross-section, alarger end of the conical cross-section region ending at the end face ofthe shaft.
 2. To a fluid dynamic bearing as claimed in claim 1 whereinthe groove pattern is defined on one or the surface of the counterplate,or the facing surface of the shaft.
 3. A fluid dynamic bearing asclaimed in claim 2 wherein the groove pattern on the surface of thecounterplate is defined to pump inward toward the axial center of theshaft.
 4. A fluid dynamic bearing as claimed in claim 1 including abearing defined along an outer surface of the conical cross-sectionalregion of the shaft.
 5. A fluid dynamic bearing as claimed in claim 1further comprising a set of grooves defined along the gap between asection of the shaft which is not conical and a facing surface of thesleeve to provide radial support for the shaft.
 6. A fluid dynamicbearing as claimed in claim 5 wherein the grooves are formed on theouter surface of the shaft.
 7. A fluid dynamic bearing as claimed inclaim 6 wherein the grooves are defined asymmetrically to pump fluid ina gap between the outer surface of the shaft and the inner surface ofthe sleeve toward the distal end of the shaft.
 8. A fluid dynamicbearing as claimed in claim 1 wherein the fluid bearing groovesincluding continuous gap extending between the outer surface of theshaft and the inner shaft of the sleeve and between the end surface ofthe shaft and a facing surface of the counterplate, the fluid bearingincluding a grooved pattern only on the outer surface of the conicalcross-section.
 9. A fluid dynamic bearing as claimed in claim 7 furthercomprising a wear-resistant surface on one of the outer surface of thegroove section of the shaft or the facing conical inner section innersurface of the sleeve, the wear-resistant layer providing a region onwhich the surfaces may rest when the shaft and sleeve are at rest.
 10. Afluid dynamic bearing as claimed in claim 7 further comprising awear-resistant surface layer on one of the end surface of the shaft orthe facing surface of the counterplate, the surface providing a restingsurface for the shaft and counterplate when they are relatively at rest.11. A fluid dynamic bearing claimed in claim 9 including means forestablishing an electromagnetic bias between the sleeve and the hub sothat the shaft rests on a selected surface of the sleeve.
 12. A spindlemotor for use in a disc drive comprising a shaft rotating in a boredefined by an inner surface of a sleeve, the shaft being supported forrotation by a fluid dynamic journal bearing comprising fluid in a gapbetween the shaft and the sleeve, the shaft supporting a hub at one end,the shaft being adapted to rotate within the sleeve supported from abase, the base including a counterplate facing an end of the shaftdistal from the one end on which the hub is mounted, one of the distalend of the shaft or the surface of the counterplate which faces the endface of the shaft having a grooved pattern thereon to maintain fluid inthe gap between the shaft and the counterplate, thereby supporting theshaft for rotation relative to the counterplate and sleeve, at leastpart of the shaft being conical in cross-section, a larger end of theconical cross-section region ending at the end face of the shaft.
 13. Toa fluid dynamic bearing as claimed in claim 12 wherein the groovepattern is defined on the surface of the counterplate.
 14. A fluiddynamic bearing as claimed in claim 13 wherein the groove pattern on thesurface of the counterplate is defined to pump inward toward the axialcenter of the shaft.
 15. A fluid dynamic bearing as claimed in claim 13including a bearing defined along an outer surface of the conicalcross-sectional region of the shaft.
 16. A fluid dynamic bearing asclaimed in claim 12 further comprising a set of grooves defined alongthe gap between a section of the shaft which is not conical and a facingsurface of the sleeve to provide radial support for the shaft.
 17. Afluid dynamic bearing as claimed in claim 16 wherein the grooves aredefined asymmetrically to pump fluid in a gap between the outer surfaceof the shaft and the inner surface of the sleeve toward the distal endof the shaft.
 18. A fluid dynamic bearing as claimed in claim 13 furthercomprising a wear-resistant surface on one of the outer surface of theconical section of the shaft or the facing conical inner section innersurface of the sleeve, the wear-resistant layer providing a region onwhich the surfaces may rest when the shaft and sleeve are at rest.
 19. Afluid dynamic bearing as claimed in claim 13 further comprising awear-resistant surface layer on one of the end surface of the shaft orthe facing surface of the counterplate, the surface providing a restingsurface for the shaft and counterplate when they are relatively at rest.20. A spindle motor for use in a disc drive comprising a shaft rotatingin a bore defined by an inner surface of a sleeve, the shaft beingsupported for rotation by a fluid dynamic journal bearing comprisingfluid in a gap between the shaft and the sleeve, the shaft supporting ahub at one end, the shaft being adapted to rotate within the sleevesupported from a base, the base including a counterplate facing an endof the shaft distal from the one end on which the hub is mounted, andmeans for supporting the shaft for rotation relative to the counterplateand sleeve, wherein at least part of the shaft is conical incross-section.